1. Field of the Invention
The invention is related to a moving map display and in particular to a moving map display in which the map data is electronically stored and the desired portion of the map is displayed on a cathode ray tube.
2. Prior Art
It is often desirable to provide to the operator of a vehicle a map showing the topographical features of the terrain immediately surrounding the vehicle. This is particularly true for the pilot of an aircraft where the terrain may be obscured by cloud cover or darkness. Some of the advanced radar systems are capable of generating an image of the terrain immediately surrounding the aircraft, however the generated map contains only limited information, and the radar image must be correlated with a navigational map in order to provide the pilot with the necessary information, such as labels identifying pertinent topographical features and recognizable landmarks. Alternatively, map displays have been developed in which the map is stored on one or more positive microphotographic transparencies such as taught in German Pat. No. 26 25 597 or by Richardson et al in U.S. Pat. No. 3,652,836. These microphotographic transparencies are projected in the operators field of view and are capable of being moved in two orthogonal directions to keep the vehicles coordinates in the center of the displayed portion of the map. In some of these systems, the transparency or even the whole projector system may be rotated so that the top of the displayed map coincides with the heading of the vehicle. Evans et al in U.S. Pat. No. 4,179,693 discloses an autonomous check point navigational system for an airborne vehicle in which flight path is periodically checked and corrected by comparing the position of terrain features on a detected map against the terrain features of an associated electronically stored reference map. The system electronically stores a plurality of reference maps, one for each check point and the addresses of the detected terrain features are modified to correct for an angular misalignment between the sensed map and the reference map. The disclosed electronic moving map display overcomes the disadvantages of the projected map and check point navigational systems and provides for increased versatility as shall be described hereinafter.